1. Technical Field
The present disclosure relates to a thermoelectric generator unit including a thermoelectric conversion element which converts heat into electric power, and also relates to a method of testing the thermoelectric generator unit.
2. Description of the Related Art
A thermoelectric conversion element is an element which can convert either heat into electric power or electric power into heat. A thermoelectric conversion element made of a thermoelectric material that exhibits the Seebeck effect can obtain thermal energy from a heat source at a relatively low temperature (of 200 degrees Celsius or less, for example) and can convert the thermal energy into electric power. With a thermoelectric generation technique based on such a thermoelectric conversion element, it is possible to collect and effectively utilize thermal energy which would conventionally have been dumped unused into the ambient in the form of steam, hot water, exhaust gas, or the like.
A thermoelectric conversion element made of a thermoelectric material will be hereinafter referred to as a “thermoelectric generator”. A thermoelectric generator generally has a so-called “π structure” where p- and n-type semiconductors, of which the carriers have mutually different electrical polarities, are combined together (see Japanese Laid-Open Patent Publication No. 2013-016685, for example). In a thermoelectric generator with the π structure, a p-type semiconductor and an n-type semiconductor are connected together electrically in series together and thermally parallel with each other. In the π structure, the direction of a temperature gradient and the direction of electric current flow are either mutually parallel or mutually antiparallel to each other. This makes it necessary to provide an output terminal on the high-temperature heat source side or the low-temperature heat source side. Consequently, to connect a plurality of such thermoelectric generators, each having the π structure, electrically in series together, a complicated wiring structure is required.
PCT International Application Publication No. 2008/056466 (which will be hereinafter referred to as “Patent Document 1”) discloses a thermoelectric generator including a stacked body of a bismuth layer and a layer of a different metal from bismuth between first and second electrodes that face each other. In the thermoelectric generator disclosed in Patent Document 1, the planes of stacking are inclined with respect to a line that connects the first and second electrodes together. PCT International Application Publication No. 2012/014366 (which will be hereinafter referred to as “Patent Document 2”), kanno et al., preprints from the 72nd Symposium of the Japan Society of Applied Physics, 30a-F-14 “A Tubular Electric Power Generator Using Off-Diagonal Thermoelectric Effects” (2011), and A. Sakai et al., International conference on thermoelectrics 2012 “Enhancement in performance of the tubular thermoelectric generator (TTEG)” (2012) disclose tubular thermoelectric generators.